1. Field of the Invention
The invention relates to a two shaft gas turbine engine and more particularly to such an engine wherein the discharge of the compressor turbine is closely coupled to a single stage power turbine through a relatively short transition annulus reducing the normal space between the power turbine and compressor turbine and providing a more axially compact unit.
2. Description of the Prior Art
Two shaft gas turbine engines are well known in the art. However, heretofore, the coupling between the high pressure compressor stage and the low pressure power turbine stage was accomplished either through a diffuser, to reduce losses, or in extremely close coupling, through stationary guide vanes. In the latter case, the blades of the compressor and power stages were closely related in both diameter and height.
In the power turbine of the present type having only one stage, the blade height and the outer diameter of each blade of the power turbine are substantially greater than the final stage of the compressor turbine so as to provide a sufficiently large discharge annular area to minimize the leaving losses (i.e., velocity) of the finally exhausted working fluid. Thus, ducting the working fluid from the small compressor turbine blade to the larger power turbine blade requires the inner and outer shroud defining the side walls of the duct to diverge. This configuration is generally typical of a diffusion section; however, in this instance the requirement for relatively close coupling did not permit sufficient axial length for a diffuser section followed by a nozzle portion to again accelerate the fluid into the power turbine.